This invention relates to variable cam arrangements for lift valves of the type used, for example, in internal combustion engines.
In conventional valve actuation arrangements for the combustion chamber valves of internal combustion engines for motor vehicles, it is known that, for optimum operation of the engine under a variety of load and speed ranges, the valve lift curves, that is, the valve open times and the maximum lift of the valves, should be variable. For this purpose, cam arrangements are known with devices positioned between a valve cam and a valve, which consequently increase the oscillating mass, as well as cams which are pivotable on a camshaft to a limited extent and which only vary the valve open time. Unless additional measures are adopted, these valve lift arrangements tend to generate noise. German Offenlegungsschrift 37 05 128 also discloses camshaft arrangements with radially adjustable cams. These arrangements include a cam having a rigid part, referred to as a displaceable slide, which is adjustable in its radial position by a control rod extending through the camshaft and an endless steel band enclosing the control rod and the rigid part and providing the cam contour. By axial displacement of the control rod, the radial position of the displaceable slide can be controlled and, at the same time, both the cam lift and the shape of the cam flanks can be varied by appropriate deformation of the steel band.
Such a cam construction has the disadvantage that it cannot adjust only the flank shape of the cam or only the maximum cam lift. In addition, a steel band which has only point support from the slide and is unsupported in other regions is hardly able to withstand the forces acting upon a cam without damage, particularly after prolonged periods of operation.